Coetzee, who finished strongly to tie for 11th at last week’s BMW Italian Open, continued his good form and finished the day two shots clear of the field in northern France.
Starting from the 10th, Coetzee dropped a shot on the 13th but immediately got back to level par, and further birdies on the 18th and third took him two under.
Two par fives in his last three holes gave him the opportunity for a grandstand finish and he took full advantage to pull clear of a group of five players — Scandinavians Eirik Tage Johansson and Thomas Norret, home player Benoit Teilleria, Andrea Perrino of Italy and Australian Matthew Zions – on three under.
His storming finish was emulated by Johansen and the Norwegian said: “I had about a four-metre putt for eagle on the last (the ninth) but just missed it.
Zions also birdied the same three holes, having started on the front nine, while Teilleria’s impressive round featured just a solitary dropped shot and Dane Norret was blemish-free.
The English quartet Daniel Denison, Sam Hutsby, Paul Dwyer and Steven Tiley followed joined by Scotland’s Craig Lee, Swede Martin Erlandsson and Australian Andrew Tampion.
Australian Daniel Gaunt is the highest-ranked player in the field and shot a disappointing 74.